Tight end Rhett Ellison, who has also blocked for Adrian Peterson from the fullback position, will miss Sunday's game with a hyperextended knee, coach Leslie Frazier said on Friday. That means the Vikings are down to a pair of options at the spot: undrafted rookie Zach Line, who is getting his first experience as a blocking back this season, and tight end John Carlson, who has done some work in the backfield since training camp started.

Carlson signed with the Vikings last year primarily as a receiving threat, but caught just eight passes for 43 yards and struggled to get on the field as an in-line tight end with Kyle Rudolph emerging as a Pro Bowl player. He's got just one catch this year, but he's been able to find some more consistent work as a run blocker, too.

Asked about the biggest adjustment to the role, Carlson said, "The lead-type runs, the downhill runs. No. 28, he's not going to slow down at all, so just get on your horse, full speed, low pad level. Fullbacks are typically much shorter than tight ends, so it's focusing on pad level and just going."

If the Vikings sustained another injury at the spot, they might not be able to use a fullback as often as they normally would. Peterson hasn't been anywhere near as effective in two-back sets this year as he was last year -- he's been in a two-back set on 24 of his 44 carries, according to ESPN Stats & Information, and is averaging just 2.0 yards per carry in those situations -- but the running back still has more yards through his first two games in 2012.

Still, another injury to the Vikings' complement of blocking backs might lead them to open up their offense a little more, particularly in the wake of Frazier's call to get Cordarrelle Patterson more involved.

Defensive tackle Fred Evans (shoulder), linebacker Erin Henderson (heel) and safety Harrison Smith (shoulder) returned to full participation on Friday after being limited during the first two practices of the week.